AbstractThis paper describes the piezoelectric phenomenon caused by the electrostrictive effect from the standpoint of material constants. First, thee, d, g, andhtypes of basic equations for the piezoelectric phenomenon including the nonlinear terms will be discussed to clarify the transformation formula between nonlinear constants.The forementioned formula is essential in the analysis of the material constants. Then the relationships among the constants before and after the polarization operation including the nonlinear constants will be clarified.It will be shown that if the deformation by polarization is small, the material withC∞symmetry which is obtained by the polarizing isotropic body has a fewer number of independent constants than a 6‐mm crystal.Finally, the foregoing results will be applied to PZT ceramics and it will be shown that the theory of electrostriction is useful in evaluating piezoelectric ceram